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Sunday December 15, 2013 6:26 AM

North America’s Arctic tundra is a vast treeless plain that blankets the northernmost reaches of
the continent. Glacial ice smothered this region until 10,000 years ago, yet it supports a
fantastic assemblage of life. During the brief Arctic summer, a potpourri of plants bursts forth:
grasses, heaths, sedges and wildflowers.

A mammalian swarm of lemmings capitalizes on the vegetative bounty. The chunky rodents can occur
in staggering numbers and are avidly sought by carnivores.

Foremost among the lemming-slayers is the snowy owl. Owls and lemmings are intertwined; as the
lemmings go, so go the owls.

Lemming populations ebb and flow in roughly four-year cycles for reasons that are poorly
understood. When the rodents abound, a snowy owl might take 1,600 in a year. That’s 190 pounds of
lemming steak.

Lemming booms and busts correlate with snowy owl spikes and crashes. More food means better
nesting success and more owlets. Lean lemming years trigger crashes in the owls.

These cycles can stimulate southward movements of owls, which are termed
irruptions (not
eruptions, as in exploding volcanoes). Too many juvenile owls can overwhelm the tundra
ecosystem, and many must fly far south to find food. Too few lemmings can also force owls to the
south.

This winter is shaping up to be a standout irruption, with numerous owls throughout the Great
Lakes region. Ohio’s first bird appeared on Nov. 22, in Trumbull County. Since then, we’ve had
about 60 others in 27 counties. Most have been along Lake Erie, from Lorain to Conneaut. Several
owls have appeared in central Ohio, and more are certain to make their way to the Buckeye
State.

Snowy owls are easy to see: They’re active during the day and frequent open spaces such as lake
shorelines and big farm fields. Thanks to the popularity of Harry Potter and his mail owl, Hedwig,
most people would recognize a snowy owl.

The birds at these latitudes are juveniles, which are often heavily barred with black. Still,
white is the dominant theme, and unsuspecting observers are amazed to encounter Hedwig in the
flesh. The owls typically hunt from ground perches but sometimes do so from telephone poles or barn
roofs.

They stick out. A big female can weigh more than 6 pounds and have a wingspan of 6 feet.

Young inexperienced owls have it tough. They’re in search of food, and barren farm fields might
resemble the tundra but are largely lacking in rodents. Vehicles present an unfamiliar threat to
the Arctic visitors. At least one Ohio owl became roadkill. Human observers — especially
photographers — should keep their distance and avoid flushing or otherwise stressing owls.

Modern irruptions are just a shadow of former invasions. The winter of 1941-42 brought 150 birds
to the Cleveland area alone. Ohio hasn’t seen such numbers for decades, and no one knows why
irruptions have tapered off — perhaps because there are fewer
Ukpik (Inuit for
snowy owl).

Polar regions remain an abstraction for most people. But the tundra produces a staggering
bonanza of biodiversity — especially birds. It is an environment to be protected, whether we see it
or not. Every now and then, the Arctic sends its spectacular ambassador, the snowy owl, to remind
us of the value of the Land of the Midnight Sun.

Naturalist Jim McCormac writes a column for The Dispatch on the first and third Sundays of the
month. He also writes about nature at www.jim mccormac.blogspot.com.